Many electroceramic components are generally soldered onto platinum in surface mounting. The possibility of surface mounting (SMD ability) can be achieved by attaching the contact surface to the ceramic components. The same applies to the production of wired components. Here too, contact surface must first be applied to the ceramic components. Wires are then attached to these contact surfaces, for example in a soldering process.
Miniaturization of electric components, for example of varistors as protection elements against overvoltages in mobile telephones, requires the production of ever smaller multicomponent elements that have several electrically conducting contact surfaces on their surfaces. Since these components generally have very small dimensions, for example edge length of about 1 mm, the contact surfaces are arranged very close to each other on the surface of the electric component, so it becomes increasing difficult to insulate the contact surfaces from each other electrically. This problem is made more acute by the fact that multilayer contact surfaces are often applied, generally by means of electroplating processes.
The adhesive strength of the electroplated contact surfaces on the ceramic component plays an essential role in this. On an untreated ceramic surface, it is so small, as a rule, that in practice it does not meet the requirements. Therefore, as a rule, a contact base is applied by means of a conducting adhesive or a conducting paste and then enameled. Additional metallic layers can then be deposited onto this contact base by electroplating.
Since some electroceramics, for example varistor ceramics based on zinc oxide, have only a low resistance, a metal layer can be completely or partially deposited onto the ceramic body in such a way that surface leak currents can appear between adjacent contact surfaces. Often, the ceramic bodies are attacked and etched by electroplating baths, which are generally acidic. This can lead, for example in the case of a varistor ceramic, to changing the grain boundaries and thereby to a change in the electric characteristics of the component.
When the electroplating liquid penetrates into the ceramic base body, its electric characteristics can also change so that components that are not overplated between two adjacent contact surfaces have an increased surface leak current.
A process for the production of multicomponent elements is known from patent document U.S. Pat. No. 6,159,768 A, in which a glass paste is applied and enameled onto the sintered ceramic body between adjacent contact surfaces. The disadvantage of this process is that the glass paste and the contact base of the contact surfaces are generally enameled in a similar temperature range at about 800° C., so this can lead to reactions between the glass paste and the conducting paste of the contact base contacting. This reaction can worsen the further deposition of additional contact surfaces by electroplating. Moreover, the reaction between the glass paste and the contact base can lead to increased surface leak currents between adjacent contact surfaces. In addition, in the processes disclosed in the U.S. patent document, only regions between contact surfaces can be provided with the glass paste so that the other regions of the ceramic body that have not provided with a passivation layer can still be etched by the acidic electroplating baths.
In addition, ceramic components are known from patent document DE 196 34 498 C2, on which protective layers of barium titanate, silicon dioxide, aluminum oxide, or glass are arranged. These protective layers have the disadvantage that they cannot be sintered together with the ceramics used for varistors, for example, and it is therefore expensive to produce such components.